The invention relates to a heating device, especially an auxiliary heating device for vehicles. The invention deals in particular with a water heating device in which water is used as a liquid heat transferring medium in the heat exchanger of the heating device.
From the German Offenlegungsschrift No. 32 08 828 and corresponding U.S. Pat. No. 4,543,943, a heating device operated with a liquid fuel, especially a heating device for vehicles using a liquid heat transfer medium has been known. Such a heating device has a burner aggregate which partially projects into a combustion chamber formed by a combustion pipe. The combustion chamber is surrounded concentrically by a heat exchanger arrangement that has an inside jacket provided with ribs and an outside jacket. Combustion gases flow through the annular chamber between the inside jacket and the burner pipe, and a liquid heat transfer medium, such as water, flows through the annular chamber between the outside jacket and the inside jacket. Generally, such water heating devices are made from parts of sheet steel which are connected together, for example, by welding.
Furthermore, recent heating devices of this construction, that is to say water heating devices, have been produced from light metal cast parts, such as cast aluminum parts. In this case, the outside jacket is developed as a separate cast part and the inside jacket is formed with the ribs as an additional, separate cast part. On the outside surface of the cast part forming the inside jacket, i.e., on the surface which limits the annular space between the outside jacket and the inside jacket, baffle plates running in a spiral shape are provided for the guidance of the liquid heat transfer medium, such as water. These spiral-shaped baffle plates forces a bipartite development of the inside jacket and the outside jacket in the case of such water heating devices. Furthermore, in the development of cast parts, it is necessary to consider oblique shapes and oversize for machining, as a result of which the shaping of the cast parts is limited. Also the tools and the molds for the cast parts are expensive which is reflected in the production costs for the cast parts. Furthermore, the casting structure is not sufficiently tight so that the cast part forming the water jacket has to be treated secondarily in order to close the pores of the casting structure. On the basis of the multipart development of the heat exchanger arrangement in the case of the known heating devices, many steps are required in the production. Also, difficulties are associated in maintaining a pressure- and watertight connection of the cast parts, since seals are provided at the points of connection that tend to leak after a while.
From the German Pat. No. 24 32 850, a heating device for vehicles has been known. In this case, however, a so-called air heating device, in which air is used as a heat transfer medium, is described. In order to decrease the dead weight of the heating device as well as for the purpose of enabling it to be produced simply and cheaply, in the case of this air heating device, the outside pipe and the inside pipe of the heat transfer arrangement together with the surrounding wall of the receiving chamber consist of a single cast part. Preferably, the casting is a light metal casting, therefore a so-called diecast part.
From the German Pat. No. 24 53 202, another form of an air heating device has been known in the case of which the inside jacket with its ribs and the wall of a receiving chamber for an electromotor that is disposed coaxially with respect to the combustion chamber, are formed by a single cast part on which the outside jacket, developed as a cast part, is molded on. The outside jacket is connected with the inside jacket only by individual ribs on the ends of the heat transfer arrangement. In the case of the use of light metal diecast parts for water heating devices, the previously cited difficulties occur with regard to the need for a secondary treatment and the tightness of the cast structure.
From the German Pat. Nos. 11 24 839 and 10 05 860 and German Utility Model No. 17 82 914, heating arrangements for motor vehicles have been known which operate and are developed as waste gas heat exchangers, and to develop parts of the heat exchanger in one piece as a diecast part, for example, the outside pipe with molded on radially running ribs and heat conductors projecting into the heating air channel. Such a diecast part is diecast from aluminum or an aluminum alloy as a straight line extruded profile. To form an outside jacket, the heat transfer arrangement has been surrounded by a steel sheet part. In this case, however, the problem exists that such extruded profile parts may lead to an overheating of the jacket so that the extruded profile part becomes too hot. In the case of water heating devices, generally sealing problems are a concern when connecting steel sheet parts and extruded profile parts, since these parts consist of different materials having different heat exchange coefficients, and the corrosion resistance is impaired. Hitherto, all these considerations have led to the fact that, in the case of the production of water heating devices, only light metal cast parts have been used which may be shaped such that the places of connection are disposed, not in the hottest area of the heat transfer arrangement, but as close as possible to the colder area of it, in order to make possible a reliable sealing of the connecting places.
Therefore, a primary object of the invention is to create a water heating device that overcomes the previously described difficulties and prejudices existent in the prior art, and, especially, provides the necessary water tightness, while being simple to produce at a reasonable cost as well as composed of as few as possible individual parts. Furthermore, such a water heating device should take up as little installation space as possible, should guarantee an efficient heat transfer and should have a dead weight that is as low as possible.
According to the invention, a heating device, especially an auxiliary vehicle heating device which may be operated with a liquid heat transfer medium, such as water, has a heat exchanger with an outer jacket formed as a single extruded profile part with ribbed inner jacket thereof.
Since, in the case of the heating device according to the invention, the outer jacket and the inner jacket provided with ribs are formed simultaneously in one operating step, according to the extrusion method, as a one-piece extruded profile part, the number of component parts which are to be put together is reduced in the case of such a water heating device. Especially in this case, separable connecting places may be avoided which hitherto lead to sealing problems in the case of water heating devices.
Also, according to the extrusion method, the shaping of the parts may be selected in a less restricted manner than in the case of cast parts, since oblique shapes and oversize for machining need not be taken into consideration. As a result, the extruded profile may be produced very thin and with even thicknesses of the wall in one operating step. Not only a material saving, but also a considerable saving in weight results, besides a surprisingly simplified production as compared to cast parts. Furthermore, the development as an extruded profile part makes possible that, in comparison to cast parts, a larger number of ribs and thinner ribs may be provided, thereby improving the degree of effectiveness of the heat transfer arrangement due to an increase of the convective heat transfer portion. As a result of the increased effectiveness, it will also be possible to shorten the length of the heat transfer arrangement and, thus of the entire heating device. Still further, additional steps of treatment for guaranteeing the tightness of the parts are omitted, since the structure of the extruded profile part is relatively tight, contrary to the structure of cast parts. Additionally, extruded profile parts may be anodized without difficulties, so that it is possible to improve the corrosion protection in a simple manner. Finally, the tools for such an extruded profile part are considerably cheaper than the molds and tools for corresponding cast parts. Also certain extrusion alloys are resistant to corrosion by the combustion gases flowing in the annular space between the burner pipe and the inside jacket.
For closing the ends of the annular chambers on the end facing away from the burner aggregate, lid parts are provided. These lid parts, which preferably are formed from deep drawn aluminum sheet parts, are welded directly onto the ends of the extruded profile part. Since, in this case, a continuous bordering exists and the place of the welded seam is easily accessible, these lid parts may be welded on without difficulty in such a way that the welded connection is reliably tight. Whenever, the lid parts are formed by deep drawn aluminum sheet parts, then the materials for the extruded profile part, aluminum or an aluminum alloy, and the lid parts to be connected should have similar characteristics, especially with regard to heat conduction and heat expansion, so that additional loads on the welds may be avoided.
With regard to the attachment of the burner aggregate to the ends of the inner and outer jackets facing the burner aggregate, the burner aggregate is provided with a flange part that will be secured to a closing ring that is attached to these ends, preferably by means of welding. In order to guarantee a reliable and tight connection, the closure ring is partially inserted into the space between the inner and the outer jackets and is provided with a welded seams between it and both the inner jacket and the outer jacket of the extruded profile part.
Preferably, the lid parts as well as the closure ring are attached by the manufacturer of the extruded profile part, so that the extruded profile part may be delivered with the lid parts and the closure ring in a condition ready for testing for tightness by the heater manufacturer.
In the case of the one-piece extruded profile part, the outer and the inner jackets are connected by way of axially running bridges. As a result, parallel water channels are formed in the annular space, between which the liquid heat transfer medium flows, without, however, having any significant influence on heat transfer, bubble formation or flow resistance.
According to a modified embodiment, the end of the extruded profile part facing the burner aggregate is developed in such a way that it serves directly for receiving the burner aggregate. Owing to this development, the use of a closure ring welded to the extruded profile part may be omitted, so that the number of parts on the heating device may be reduced still further, because the burner aggregate may be mounted onto the molded-on receiving flange of the extruded profile part directly. For the attachment of the burner aggregate by screws, preferably, through-holes are developed on the extruded profile part.
It is also possible to adapt the outside contour of the extruded profile part to the shape of the burner aggregate and of an optionally provided cover-up hood by, for example, selecting a cross section for the extruded profile part approaching a square. As a result, the production of such a device is simplified and made cheapter since, for example, the processing and welding on of an intermediate flange to the burner head and/or at the end of the extruded profile part is omitted. Also, the inlet and outlet connection for the liquid heat transfer medium may be disposed in such a way that they are formed integrally, for example, as a part of the lid so that it will not be necessary to weld these inlet and outlet connections to the extruded profile part in a separate operating step.
In addition, strips are formed in the extruded profile part for the attachment of a cable cover-up hood and/or bases serving as supports on the extruded profile part, so that no separate attachment for a support will be necessary. Naturally, it will also be possible to mold additional means of attachment onto the extruded profile part or possibly to develop cable channels, all of which are integrated into it in a single operating step with the production of the extruded profile part in order to shorten the production and mounting time.
In order to reduce the dead weight of the heating device as far as possible, and in order to increase the transfer of heat, a light metal or a light metal alloy, preferably an aluminum or an aluminum alloy, is used for the production of the extruded profile part. Furthermore, this material is easily anodizable in order to improve the corrosion resistance of the extruded profile part.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.